The invention relates to a structural part including a portion that is made of thermostructural material cooled by fluid circulation.
The invention finds applications in making structures that are exposed in operation to very high heat flux or to aggressive environmental conditions at very high temperatures. It relates in particular to wall structures that are exposed to hot gas flows, e.g. wall structures for the combustion chambers of jet or rocket engines, or wall structures exposed to intense heating, e.g. wall structures of spaceplane vehicles, particularly during atmosphere reentry stages, or indeed wall structures that form heat screens, e.g. in nuclear fusion reactors.
Because of their mechanical properties which make them suitable for constituting structural elements, and because of their capacity to retain these properties up to high temperatures, thermostructural composite materials are commonly used in such applications. Specifically, the materials are carbon-carbon (C/C) composite materials comprising carbon fiber reinforcement densified with a carbon matrix, and ceramic matrix composites (CMCs) comprising reinforcement of refractory fibers (e.g. carbon or ceramic) densified by a ceramic matrix.
When thermostructural composite materials are used under very severe environmental conditions (intense heat flux or an atmosphere that is aggressive, in particular that is oxidizing), it is necessary to limit the surface temperature thereof in order to obtain satisfactory lifetime.
A conventional method of cooling consists in circulating a cooling or xe2x80x9cheat-conveyingxe2x80x9d fluid.
Proposals have been made to form fluid circulation passages within a composite material or in its rear face. Because thermostructural composite materials inevitably present residual porosity because of the way in which they are made, it is necessary to guarantee fluid tightness for the walls of the fluid circulation passages. Reference can be made for example to U.S. Pat. No. 5,583,895.
Proposals have also been made to connect a piece of composite material to a substrate made of metal, e.g. copper, which is cooled by a circulating cooling fluid. A problem which is difficult to solve is that of bonding together two parts that have coefficients of thermal expansion that are significantly different from each other. Reference can be made in particular to document WO 98/03297.
Those parts of known structure therefore present difficult problems of preparation. In addition, they are relatively heavy, which at least in certain applications constitutes a severe drawback.
An object of the invention is to provide a structural part having a piece of thermostructural composite material cooled by fluid circulation and which can be prepared without raising the same difficulties as in the prior art.
Another object of the invention is to propose such a part which is substantially lighter than in the prior art.
These objects are achieved with a structural part comprising a piece of thermostructural composite material connected to a metal wall provided with fluid circulation passages, in which part the composite material piece comprises a plate and a plurality of stiffeners formed integrally with the plate and situated on one side thereof, being spaced apart from one another, and the metal wall is fixed to the end edges of the stiffeners.
Thus, the piece of thermostructural composite material withstands heat flux and mechanical loads, and radiates from its rear face towards the metal piece through the gaps between the stiffeners. In contrast with the prior art, this decoupling between thermal and mechanical effects simplifies manufacture of the structural part.
In particular, the following advantages are obtained:
the plate of thermostructural composite material stiffened by the stiffeners can itself be thin, so as to constitute merely a skin, imparting lightness to the assembly while still performing its structural function;
since the plate of composite material is exposed to the heat flux via its front face opposite from its face provided with the stiffeners, heat transfer takes place by conduction through the plate, by radiation in the gaps situated between the stiffeners from the back face of the plate to the metal wall, and by forced convection of the fluid travelling in the passages of the metal wall;
the metal wall and the piece of thermostructural composite material are assembled together solely via the end edges of the stiffeners, i.e. in discontinuous manner and at the locations that are furthest from the plate exposed to the heat flux; as a result, thermomechanical stresses are minimized and assembly is simplified;
since the structural function is performed by the piece made of thermostructural composite material, it is possible to use a thin metal wall having fluid circulation pipes fitted thereto, thus minimizing the overall mass of the part; and
the piece made of thermostructural composite material and the metal wall can be assembled together during final assembly of the part, e.g. by brazing or mechanically, thereby making it possible to manufacture structures of complex shape, e.g. having dual curvature.
The invention also seeks to provide a method of manufacturing a part having the structure as defined above.
In the method, a fiber preform for the composite material piece is made by assembling together preform elements corresponding to the plate and to the stiffeners, the preform is densified so as to obtain the composite material piece, and the metal wall is fixed to the end edges of the stiffeners.